The reduction of nitro-alkylbenzene to the corresponding hydrazo compounds is well known in the prior art. The most well known reduction involves the reduction of nitro-alkylbenzenes in the presence of zinc metal and an alkaline media by a batch process. This reduction is not catalytic and therefore consumes large quantities of zinc metal. In addition, the by-products of this reaction produce an environmental problem of disposal of zinc compounds.
Various catalytic processes have been developed for the preparation of aromatic hydrazo compounds. The Germans, in the late ninteenth century, reported the use of a palladium on carbon catalyst in the presence of aqueous potassium hydroxide to produce hydrazobenzene from nitrobenzene. Nitrobenzene and chlorinated derivatives of nitrobenzene have been investigated using catalytic reduction processes.
In U.S. Pat. No. 2,233,129 a process is disclosed for the reduction of ortho-nitrotoluene to a mixture of hydrazotoluene and o-toluidine. The patent discloses that the reaction could be performed in a solvent consisting of an oxygen containing, nonacidic organic compound of from 1 to 7 carbon atoms. The solvent would be utilized in conjunction with an active noble metal catalyst in an alkaline medium. Specifically, the examples show the use of caustic soda and palladium black supported on activated carbon. In addition, the use of an organic solvent such as ethanol was specifically set forth for the production of o-tolidine. However, this recited process generally produces a mixture of hydrazotoluene, ortho-toluidine and certain amounts of azotoluene, rather than a high yield of hydrazotoluene to the exclusion of the other compounds.
The use of aqueous ethyl alcohol solvents for the production of chlorohydrazobenzene has been described in U.S. Pat. No. 3,156,724. The process utilizes noble metal catalysts supported on carbon such as palladium, or platinum and a naphthalene inhibitor such as naphthoquinone. An alkaline reaction medium is provided by the use of sodium or potassium hydroxide. Characteristically, ortho-nitrochlorobenzene is converted to ortho-dichlorohydrazobenzene by catalytic reduction in the above described reaction medium.
The utility of hydrazobenzene compounds such as ortho-hydrazotoluene is documented in U.S. Pat. No. 3,253,010 wherein the hydrazobenzene compounds are reacted with phosgene to create isocyanates which are useful prepolymer components of urethane polymers.
In U.S. Pat. No. 3,260,750 a process for the production of hydrazobenzenes is set forth. The patent sets forth the typical catalysts and reaction media known to date for the production of hydrazobenzenes including, the use of palladium, platinum or rhodium and alcoholic solvents, preferably methanol. Sodium hydroxide is utilized to provide the alkaline medium for the reduction of the nitrobenzene to the respective hydrazobenzene. The patent teaches that the reaction should be conducted in a two-stage process wherein the temperature is controlled from 0.degree. C. to 40.degree. C. in the first stage and from 60.degree. C. to 100.degree. C. in the final stage.
In U.S. Pat. No. 3,694,509 it is disclosed that in a neutral reaction medium using a platinum on carbon catalyst, improved yields of N-arylhydroxyl amines can be obtained in the presence of dimethyl sulfoxide.
In Japanese Patent Publication No. 50-89253, the hydrogenation reduction of nitrobenzenes to hydrazobenzenes is taught wherein a caustic alkali, water, a platinum catalyst, a quinone compound and a small quantity of dispersing agent are placed in a reactor under hydrogen gas and heated for a predetermined time until the reaction is complete.
The prior art fails to provide a process for producing hydrazotoluene compounds in superior high yields in a manner in which the reaction product is easily recoverable.